EP1331749B1 - Multiple signal transmission on a coaxial cable - Google Patents

Description

The present invention relates to a method and a signal processing device for their transmission over a coaxial cable.

The figure 1 schematically represents a device for receiving and processing modulated analog signals transmitted over the air, for example signals corresponding to video images. This architecture comprises a reception unit 10 which receives, via a receiving antenna, a modulated analog signal corresponding to an electromagnetic wave transmitted over the air. The receiving unit 10 comprises a low noise LNB block 11 (Low Noise Block) which performs preprocessing on the received modulated signal. The pre-processed modulated signal is transmitted to a signal processing unit 12 via a coaxial cable 14. The processing unit 12 comprises a demodulation block DEMOD 15 which extracts a modulated signal "useful" in the modulated signal transmitted on the coaxial cable 14 and demodulates the "useful" signal extracted. The demodulated "useful" signal may, for example, be used for displaying video images on a television screen. In this case, the reception unit 10 is located at the receiving antenna and the processing unit 12, on which the viewer must be able to act, is located at the television set.

The figure 2 represents a schematic example of the spectrum of a modulated analog or digital signal received by the LNB block 11. The signal has an initial frequency band IBW which extends, for example, between 10.7 GHz and 12.75 GHz, which corresponds to a frequency band generally used for the transmission of signals between a satellite and a receiving station on the ground.

The initial frequency band IBW is divided into frequency channels. The width ΔB of the frequency band of each channel may vary, for example, from 24 MHz to 36 MHz, four channels CH1 to CH4 being represented for illustrative purposes on the figure 2 . The initial modulated signal received by the reception unit corresponds to the sum of modulated "useful" signals. The frequency band of each modulated "useful" signal is included in one of the frequency channels CH1 to CH4. The frequency channels CH1 to CH4 associated with "useful" signals of the same polarization are distinct. However, the initial modulated signal may correspond to the sum of signals whose polarizations are different. The polarization can be, for example, rectilinear (horizontal or vertical), or circular (right or left). Since different polarization waves can be easily separated in the same signal, it is possible to transmit in the same initial signal "useful" signals of different polarization associated with overlapping frequency channels.

• amplifier les signaux reçus avec le plus petit facteur de bruit possible, typiquement de l'ordre du décibel ;
• sélectionner la polarisation du signal, par exemple horizontale ou verticale ;
• convertir les signaux reçus de la bande de fréquence initiale IBW en une bande de fréquence, appelée bande de transmission, adaptée à la bande passante du câble coaxial 14 et à la bande de fréquence de l'unité de traitement 12 (de façon typique entre 950 MHz et 2150 MHz), et
• limiter les signaux à transmettre à une certaine bande de fréquence.

The main functions of the LNB block 11 are:

• amplifying the received signals with the smallest possible noise factor, typically of the order of the decibel;
• select the polarization of the signal, for example horizontal or vertical;
• converting the signals received from the initial frequency band IBW into a frequency band, called a transmission band, adapted to the bandwidth of the coaxial cable 14 and to the frequency band of the processing unit 12 (typically between 950 and MHz and 2150 MHz), and
• limit the signals to be transmitted to a certain frequency band.

The figure 3 schematically represents an example of a conventional architecture of the LNB block 11. The LNB block 11 is connected to an antenna 16 receiving the initial signal transmitted over the air. The antenna 16 comprises two foci 17, 18. Each focus 17, 18 captures an initial signal of polarization determined in the initial frequency band IBW. For example, focus 18 may pick up an initial signal horizontally polarized, and focus 17 an initial signal vertically polarized. Each focus 17, 18 is connected via an amplifier 20, 21 to a first IRF filter 22 (Image Rejection Filter). Amplifiers 20, 21 may consist of low noise field effect transistors. A control unit 23 drives the amplifiers 20, 21 to select one of the two initial signals with determined polarization.

The initial signal with determined polarization is then transmitted to a mixer 25 which mixes the initial signal with a mixing frequency f _M , emitted by a frequency synthesizer 26, to move the initial frequency band IBW from the initial signal to the transmission band . The function of the IRF filter 22 is to prevent spurious signals from disturbing the signal obtained following passage through the mixer 25. The frequency f _M is a function of the initial frequency band IBW and of the transmission band.

The signal thus mixed is transmitted to a bandpass filter BPF 27 which limits the frequency band of the signal to be transmitted to minimize the amount of power on the coaxial cable 14. The mixed and filtered signal is finally amplified by an amplifier 28 before the be transmitted over the coaxial cable 14.

The width of the initial frequency band IBW may be wider than the transmission band. In this case, the frequency synthesizer 26 can produce several mixing frequencies. Each mixing frequency is adapted so that, during the mixing operation, a particular portion of the initial frequency band IBW, of width similar to the width of the transmission band, is shifted to the frequencies of the transmission band. The choice of the mixing frequency is then determined by the control unit 23 as a function of control signals transmitted by the processing unit 12 and transmitted to the LNB block 11 by the coaxial cable 14.

A processing unit may comprise several demodulation blocks so as to simultaneously process a plurality of "useful" signals of the same polarization that are extracted from the signal transmitted by the coaxial cable.

However, it may be desirable for a processing unit to process several "useful" signals of different polarizations in parallel. Similarly, it may be desirable for a processing unit to process in parallel a plurality of "useful" signals from an initial signal having an initial frequency band wider than the transmission band, the "useful" signals being derived from portions of different initial frequency band. Finally, it may be desirable for a processing unit to be able to process several "useful" signals from initial signals having distinct initial frequency bands in parallel, in particular in the case of a so-called multi-orbit antenna which has a plurality of oriented focal points. to receive radio signals of distinct initial frequency bands.

The device of the figure 1 is no longer suitable. Indeed, at the same time, the signal transmitted on the coaxial cable 14 can come only from a single initial signal and have only one specific polarization. In addition, when the initial frequency band is wider than the transmission band, the signal transmitted on the coaxial cable 14 can only correspond to a single portion of the initial frequency band.

It is then necessary to provide several LNB blocks and to connect each of them to the processing unit 12 by a dedicated coaxial cable. Each LNB block then transmits, on the associated coaxial cable, a signal of a certain polarization, and which corresponds to a determined initial frequency band signal (and possibly to a certain portion of the frequency band of the initial signal).

The multiplication of coaxial cables is a significant cost since each coaxial cable corresponds to at least four connectors, and the processing unit 12 must include switches associated with each cable. In addition, the installation and maintenance of cables are expensive.

The document WO 99 37092 describes a system for distributing television signals, audio signals, digital audio signals and / or video signals.

The present invention aims at transmitting on a single coaxial cable, at the same time, "useful" signals that may have different polarizations, and / or be derived from initial signals of distinct initial frequency bands, and / or, when the band initial frequency is wider than the transmission band, be derived from distinct portions of the initial frequency band.

To achieve this object, the present invention provides a receiver that can receive several initial modulated signals in the same initial frequency band and / or separate initial frequency bands and produce a modulated signal in a transmission band to be transmitted over a coaxial cable, the receiver having a selector capable of selecting a plurality of signals from the received signals; for each selected signal, a mixer capable of transforming the selected signal into a signal at least partly in the transmission band, and a filter adapted to extract from the transformed signal a signal associated with a portion of the transmission band among several portions of the transmission band at least partly distinct; and means for forming the modulated signal in the transmission band from the signals associated with the transmission band portions.

Each mixer is connected to a frequency synthesizer specific to produce a determined mixing frequency, the determined frequency being a function of the portion of the transmission band and the selected signal.

The receiver has reception points, associated with an antenna, each reception center being able to receive an initial modulated signal, and intermediate mixers, each intermediate mixer being able to transform the initial signal received by a reception focus into an intermediate signal in an intermediate frequency band different from the transmission band, the selector receiving the intermediate signals.

The receiver comprises a control unit receiving control signals via the coaxial cable and driving the frequency synthesizers according to the control signals for the production of the mixing frequency, and the selector for the selection of the received signals.

According to one embodiment of the invention, the filters are bandpass filters of distinct bandwidths, and for a first filter whose bandwidth is at frequencies greater than those of the bandwidth of a second filter, the difference between the gain of the second filter and the gain of the first filter at the upper limit frequency of the bandwidth of the second filter is greater than 30 decibels, and the difference between the gain of the first filter and the gain of the second filter at the limit frequency lower bandwidth of the first filter is greater than 30 decibels.

According to one embodiment of the invention, the frequency synthesizer is able to produce a mixing frequency in a frequency band whose width is greater than the width of the initial frequency band or the sum of the widths of the frequency bands. different initial frequencies.

According to one embodiment of the invention, at least one frequency synthesizer is adapted to transmit directly to the corresponding filter a periodic signal of determined frequency and power.

The present invention also provides a method of transforming a plurality of modulated signals received in the same initial transmission band and / or distinct initial frequency bands into a modulated signal in a transmission band, comprising the steps of selecting a plurality of signals from among the received signals; for each selected signal, transforming the selected signal into a signal at least partly in the transmission band, and extracting from the transformed signal a signal associated with a portion of the transmission band among several portions of the transmission band at least in part distinct; and forming the modulated signal in the transmission band from the signals associated with the portions of the transmission band.

Prior to the selection step, each received modulated signal is transformed into an intermediate signal in an intermediate frequency band different from the transmission band.

Each selected signal is converted into a signal at least partly in the transmission band by mixing the selected signal with a mixing frequency depending on the selected signal and the portion of the transmission band.

Each selected signal can be amplified by a variable gain before being transformed and / or after having been transformed into a signal at least partly in the transmission band, the gain depending on the selected signal.

The invention also relates to a method of testing a receiver according to the invention connected, via the coaxial cable, to a processing unit adapted to process the modulated signal in the transmission band provided by the receiver. in a normal operating mode, comprising the steps of the transmission by the processing unit to the receiver of a request associated with a determined frequency; the transmission by the receiver of a periodic signal corresponding to the reception by the processing unit of a periodic signal at the determined frequency; the determination by the processing unit of the power of the periodic signal received at the determined frequency; and determining by the processing unit the power attenuation of the coaxial cable from the power of the periodic signal received at the determined frequency and the power of the periodic signal transmitted by the receiver.

According to one embodiment of the invention, the receiver transmits successively on the coaxial cable, on receipt of requests sent by the processing unit, periodic signals at different fixed frequencies.

According to one embodiment of the invention, the receiver transmits on the coaxial cable a periodic signal at a first frequency corresponding to the reception by the processing unit of a periodic signal at the determined frequency, and a periodic signal to a second frequency different from the first frequency, the difference between the first and second frequencies being representative of the power of the periodic signal at the first frequency transmitted by the receiver.

According to one embodiment of the invention, each frequency synthesizer of the receiver is adapted to transmit directly to the corresponding filter a periodic signal and the receiver transmits to the processing unit by the coaxial cable a signal corresponding to the sum of periodic signals. provided by the frequency synthesizers, each periodic signal being at a frequency equal to the average frequency of one of the transmission band portions.

• la figure 1, mentionnée précédemment, représente de façon schématique un dispositif classique pour la réception et le traitement de signaux hertziens ;
• la figure 2, mentionnée précédemment, illustre un exemple de représentation spectrale d'un signal hertzien ;
• la figure 3, mentionnée précédemment, représente un exemple d'architecture classique d'un bloc à faible bruit ;
• la figure 4 représente, de façon schématique, une architecture pour la réception et le traitement de signaux hertziens selon la présente invention ;
• la figure 5 représente les spectres de plusieurs signaux illustrant le principe de l'invention ;
• la figure 6 représente un exemple de réalisation de l'unité de réception de la figure 4 ;
• la figure 7 représente un exemple de réalisation d'un élément de la figure 6 ;
• la figure 8 représente l'allure du gabarit d'un filtre passe-bande utilisé dans la présente invention ; et
• la figure 9 représente des exemples de valeur de gabarit du filtre passe-bande de la figure 8.

This and other objects, features, and advantages of the present invention will be set forth in detail in the following description of particular embodiments. made in a non-limiting manner in relation to the appended figures among which:

• the figure 1 , mentioned above, schematically represents a conventional device for receiving and processing radio signals;
• the figure 2 , mentioned above, illustrates an example of a spectral representation of a radio signal;
• the figure 3 , mentioned above, represents an example of a conventional architecture of a low noise block;
• the figure 4 schematically shows an architecture for receiving and processing radio signals according to the present invention;
• the figure 5 represents the spectra of several signals illustrating the principle of the invention;
• the figure 6 represents an embodiment of the reception unit of the figure 4 ;
• the figure 7 represents an embodiment of an element of the figure 6 ;
• the figure 8 represents the shape of the template of a bandpass filter used in the present invention; and
• the figure 9 represents examples of the template value of the bandpass filter of the figure 8 .

As illustrated on the figure 4 , the device comprises a reception unit 10 connected by a coaxial cable 14 to a processing unit 12. For example, the processing unit 12 comprises four demodulation blocks DEMODA to DEMODD, each demodulation block DEMODA to DEMODD including, among others, a channel selector and a demodulator.

The reception unit 10 comprises three low-noise blocks LNB1, LNB2, LNB3, which have a similar architecture to that of the LNB block 11 shown in FIG. figure 2 . More specifically, each low-noise block LNB1 to LNB3 is adapted to receive a radio signal in an initial frequency band and output a signal of a determined polarization in an intermediate frequency band which is less than the initial frequency band and greater than the transmission band, or similar to the transmission band. For example, the intermediate frequency band is approximately 2 to 4 GHz when it is lower than the initial frequency band and greater than the transmission band or 0.9 to 2.15 GHz when it is similar to the transmission band. Each low-noise block LNB1 to LNB3 is connected to a selector 30, itself connected to four mixing and filtering blocks MFA to MFD. The selector 30 may transmit any of the outputs of the low noise blocks LNB1 to LNB3 to any of the mixing and filtering blocks MFA to MFD.

The figure 5 illustrates the principle of the invention. From top to bottom are represented schematically the spectra SLNB1 to SLNB3 of the signals respectively emitted by the blocks LNB1 to LNB3. For the SLNB1 and SLNB2 spectra, the spectrum of a "useful" signal, respectively S1 and S2, is shown by way of illustration. For spectrum SLNB3, the spectra of two "useful" signals S3 and S4 are represented. One of the signals emitted by the blocks LNB1 to LNB3 is transmitted by the selector 30 to each of the blocks MFA to MFD. For example, the blocks MFA and MFB are respectively transmitted the signals transmitted by the LNB1 and LNB2 blocks, and the MFC and MFD blocks is transmitted the signal transmitted by the LNB3 block.

Each MFA block MFD performs a signal shift operation from the intermediate frequency band in a frequency band that completely or partially overlaps the transmission band. The intermediate frequency band is chosen to limit the formation of spurious signals during the shifting operation.

Each MFA to MFD block then filters the shifted signal and retains a portion of the shifted frequency band included in the transmission band and including the wanted signal spectrum. The different portions of the transmission band are respectively referenced SA to SD for the mixing and selection blocks MFA to MFD.

The various signals associated with the portions of transmission band SA to SD are added to form a signal whose frequency band BS substantially corresponds to the transmission band. This signal is then transmitted to the processing unit 12 by the coaxial cable 14. Each demodulator block DEMODA to DEMODD is adapted to extract and process in the transmission band signal a signal corresponding to one of the portions of the band. transmission.

The figure 6 represents an example of a more detailed architecture of the reception unit of the figure 5 . On the left of the figure are only represented the mixers 35, 36, 37 associated with the blocks LNB1 to LNB3. By way of example, the mixing frequencies fed to the mixers 35, 36 are produced by a single frequency synthesizer 38. The mixing frequency fed to the mixer 37 is produced by a frequency synthesizer 39.

The selector 30 receives as input the signals emitted by the blocks LNB1 to LNB3 and is connected at the output to four blocks MFA to MFD and to a mixer block M.

Each mixing and selection block MFA to MFD comprises, in series, a mixing block MA to MD, a bandpass filter BPFA to BPFD and an isolation amplifier 40A to 40D. The signals produced by the four mixing and selection blocks MFA to MFD are added and then amplified by a fixed gain amplifier 45 before being transmitted by the coaxial cable 14. The signal from the mixer block M is amplified by an amplifier 46. and transmitted by an auxiliary coaxial cable 47. A control unit 48 is connected by a first control bus 50 to the different mixer blocks M, MA to MD. The control unit is also connected to the coaxial cables 14, 47 by a second control bus 51.

The figure 7 shows in more detail the architecture of mixing blocks M, MA to MD. Each mixer block comprises, connected in series, a first fixed gain amplifier 52, a first variable gain amplifier 53, a mixer 54, a second variable gain amplifier 55 and a second fixed gain amplifier 56. The mixer 54 is powered by a frequency The mixing block M, MA to MD also comprises a control unit 58 connected to the first control bus 50 and able to control the selector 30, the frequency synthesizer 54, and the amplifiers. at variable gain 53, 55.

The operation of the device Figures 6 and 7 is the next. According to the "useful" signals S1 to S4 to be processed by the demodulation blocks DEMODA to DEMODD, the processing unit 12 transmits control signals to the control unit 48, for example according to the communication protocol FSK (Frequency Shift Keying) or the protocol known as DiSEqC (Digital Satellite Equipment Control). The control unit 48 consequently transmits control signals to the control units 58 of one or more mixer blocks M, MA to MD, via the first control block 50, for example according to the communication protocol. known as I ² C (Integrated Circuit Control).

The control unit 58 having received the control signals then drives the selectors 30 so that one of the signals produced by the LNB1 to LNB3 blocks is transmitted to the associated mixer block M, MA to MD. The control unit 58 also drives the frequency synthesizer 57 of the mixer block MA to MD to produce a suitable mixing frequency so that the signal received by the mixer block MA to MD is correctly shifted in frequency so that the frequency band of the "useful" signal S1 to S4, after passing through the mixer 54, being in the bandwidth of the bandpass filter BPFA to BPFD associated with the mixing block MA to MD. For the mixer block M, the control unit 58 controls the frequency synthesizer 57 of the mixer block M to produce a mixing frequency adapted so that the signal received by the mixer block M is correctly shifted in frequency so that the frequency band of the signal emitted by the mixer unit M is contained in the bandwidth of the auxiliary coaxial cable 47, generally the transmission band.

The variable gain amplifiers 53, 55 make it possible to adjust the amplification of the signal upstream or downstream of the mixer 54. For example, if the initial signal is of low amplitude, it may be preferable to amplify it upstream of the mixer. If the amplitude of the initial signal is sufficient, but the coaxial cable is of long length, it may be preferable to amplify the signal downstream of the mixer 54 to avoid clipping phenomena during the offset operation. . Each mixer block M, MA to MD may consist of an integrated circuit.

The auxiliary coaxial cable 47 is provided so as to allow the use of the reception unit according to the invention with a conventional processing unit which can not process the signal transmitted on the coaxial cable 14. Indeed, the signal transmitted on the coaxial cable 47 is similar with the signal from the LNB block of the figure 3 .

The figure 8 represents an example of the templates of two bandpass filters, for example BPFA and BPFB, whose bandwidths are similar. Each filter has a bandwidth, WA, WB, centered on an average frequency f _A , f _B , and limited by a higher frequency f _ASUP , f _BSUP and a lower frequency f _AINF , f _BINF . The templates are determined such that the gain of the BPFB filter at the frequency _ASUP has a difference ΔGA of at least 30 dB with the gain of the BPFA filter, and that the gain of the BPFA filter at the frequency f _BINF has a difference ΔGB at least 30 dB with the gain of the BPFB filter.

The figure 9 As an example, there are numerical values of the characteristics of the templates of the bandpass filters of mixing and selection blocks in three different configurations. The first configuration includes two mixing and selection blocks (bandpass filters BPF1 and BPF2), the second configuration comprises four mixing and selection blocks (bandpass filters BPFA to BPFD), which corresponds, for example, to the architecture of the figure 4 and the third configuration comprises six mix and select blocks (BPFI and BPFVI bandpass filters). The second column represents the average frequency f of the bandwidth of each bandpass filter. The third column represents the width W of the bandwidth of each bandpass filter. The fourth column represents the lower frequency f _INF of the bandwidth of each bandpass filter and the fifth column represents the upper frequency f _SUP of the bandwidth of each bandpass filter.

As it appears on the figure 8 Band pass filter bandwidths in all configurations are larger than the usual channel bandwidths (about 24 to 36 MHz). Band pass filters can be made discretely.

The present invention has many advantages.

It allows the transmission on the same coaxial cable of "useful" signals may have different polarizations. Indeed, the signals from the low noise blocks LNB1 to LNB3, which will be processed by the mixing and filtering blocks MFA to MFD, may have distinct polarizations.

In addition, it allows the transmission on the same coaxial cable of "useful" signals that can be derived from signals of different initial frequency bands. Indeed, two signals emitted by two blocks LNB1 to LNB3 may have distinct initial frequency bands.

In addition, it allows the transmission on the same coaxial cable of "useful" signals that may, when the initial frequency band is wider than the transmission band, be derived from distinct portions of the initial frequency band. Indeed, two signals emitted by two blocks LNB1 to LNB3 may correspond to distinct portions of the initial frequency band of the same signal.

The present invention makes it possible to compactly form a reception unit of reduced volume.

The present invention finally makes it possible to produce bandpass filters by relatively inexpensive discrete components.

According to another embodiment of the invention, the frequency synthesizer of each mixing block, which shifts the signal from the intermediate frequency band to the final frequency band, provides a mixing frequency, called a second mixing frequency, which may vary in a frequency band wider than the initial band. The range of the second mixing frequency is such that a single frequency synthesizer can be used to convert the signal from the initial frequency band to the intermediate frequency band. This synthesizer provides the same determined mixing frequency, called the first mixing frequency, for all the signals from the low noise blocks. The conversions of the signal to be processed from the initial frequency band to the intermediate frequency band and from the intermediate frequency band to the final frequency band may be two infra-heterodyne or supra-heterodyne conversions. The bandpass filter associated with a mixing block has a bandwidth adapted to select, in the signal supplied by the mixer unit, the "useful" signal. The selected "useful" signals are then added to form the transmitted signal on the coaxial cable as previously described.

For example, if the initial frequency band is between 10.7 GHz and 12.75 GHz, the first mixing frequency can be 13.25 GHz and the second mixing frequency can be chosen between 1.9 GHz and 4.3 GHz. In this example, the conversions of the received signal from the initial frequency band to the intermediate frequency band and from the intermediate frequency band to the final frequency band are supra-heterodyne conversions. The spectrum of the signal to be processed is therefore inverted twice.

The width of the bandpass filter associated with a mixer block can be chosen such that the lower frequency of the bandpass filter corresponds to the highest frequency of the final frequency band when the second mixing frequency is set to its value. the lowest. In the present example, the lower frequency of the bandpass filter is 1.4 GHz when the second mixing frequency is 1.9 GHz. The upper frequency of the bandpass filter corresponds to the lowest frequency when the second mixing frequency is set to its highest value. In the present example, the upper frequency of the bandpass filter is 1.75 GHz when the second mixing frequency is 4.3 GHz. For a coaxial cable having a bandwidth between 950 MHz and 2150 MHz, three mixer blocks and the associated filters may be provided in the present example.

This embodiment of the invention provides additional advantages.

When the frequency band of the second mixing frequency is sufficiently wide, this embodiment allows the use of a single first mixing frequency for converting the signal to be processed from the initial frequency band to the intermediate frequency band. . A single synthesizer can then be used to provide the first mixing frequency. The number of low noise blocks can then be reduced to the number of possible polarizations of the signal to be processed. A smaller and lighter housing may further be provided to receive the receiving unit, and the shields of protection of lines carrying high voltage signals and the breeder are simplified.

This embodiment can easily be made compatible with a reception unit according to the prior art which transmits on the coaxial cable a single signal occupying the entire transmission band. A large additional bandpass filter, for example having a bandwidth equal to the transmission band, is provided in parallel with a "normal" bandpass filter connected to a mixer block. In normal operation, the broad bandpass filter is disabled. When the receiving unit is to function as a reception unit according to the prior art, the broad bandpass filter is switched and all mixer blocks are switched off, with the exception of the mixer block connected to the large additional bandpass filter. . The "normal" bandpass filter connected to the activated mixer block is also disabled. The second mixing frequency of the activated mixer block is chosen so that the conversions of the signal to be processed from the initial frequency band to the intermediate frequency band and from the intermediate frequency band to the final frequency band are equivalent to one single conversion with an equivalent mixing frequency equal to 9.75 GHz or 10.6 GHz, in the present example, according to the band of the received signal that it is desired to transmit on the coaxial cable. In the previous example, to obtain an equivalent mixing frequency equal to 9.75 GHz, the second mixing frequency is set at 3500 MHz. To obtain an equivalent mixing frequency equal to 10.6 GHz, the second mixing frequency is set at 2650 MHz.

This embodiment is therefore compatible with a processing unit according to the prior art without requiring the addition of another coaxial cable or without modifying the breeder.

According to another embodiment of the invention, not shown, the reception unit can operate in a control mode. In such a mode, the frequency synthesizer 57 of one of the mixing blocks MA to MD no longer provides a mixing frequency to mixer 54 of the mixing block as previously described, but directly to the BPFA BPFD bandpass filter connected to it. to the mixer block, via a frequency divider. This frequency synthesizer is subsequently called a control synthesizer when performing a control operation.

The frequency of the signal emitted by the frequency synthesizer 57 is divided when this signal is directly transmitted to the bandpass filter BPFA to BPFD so that the latter receives a signal having a fixed frequency belonging to the transmission band.

• l'unité de traitement 12 transmet à l'unité de contrôle 48 de l'unité de réception 10 une commande pour éteindre l'ensemble des blocs mélangeurs MA à MD, par exemple en coupant leur alimentation. La commande est transmise par exemple selon le protocole connu sous la marque DiSEq1. Il s'agit d'un protocole d'échange de données dans une seule direction à savoir depuis l'unité de traitement 12 vers l'unité de réception 10. Sa mise en oeuvre est plus simple que celle du protocole connu sous la marque DiSEq2 qui est adapté à un échange de données bidirectionnel entre l'unité de traitement 12 et l'unité de réception 10 ;
• un des blocs de démodulation DEMODA à DEMODD de l'unité de traitement 12, ou l'unique bloc de démodulation, est piloté de façon à extraire du signal reçu depuis le câble coaxial un signal à une fréquence fixe déterminée, appelée fréquence de contrôle, par exemple 1700 MHz. On vérifie alors que la puissance du signal reçu à la fréquence de contrôle est très faible ;
• l'unité de traitement 12 transmet à l'unité de contrôle 48 une nouvelle commande pour que le synthétiseur de contrôle fournisse au filtre passe-bande un signal de fréquence fixe. La fréquence du signal reçu par le filtre passe-bande est légèrement supérieure à la fréquence de contrôle, par exemple de 2 MHz pour tenir compte d'un décalage en fréquence systématique présent au niveau du bloc de démodulation ;
• le bloc de démodulation de l'unité de traitement 12 extrait à nouveau le signal à la fréquence de contrôle. On détermine alors la puissance du signal reçu à la fréquence de contrôle, ou puissance reçue P_R ;
• l'atténuation du câble est obtenue en déterminant la différence entre la puissance émise au niveau de la sortie de l'unité de réception 10 (c'est-à-dire au niveau de la connexion entre l'unité de réception 10 et le câble coaxial 14), appelée puissance transmise P_T, et la puissance reçue P_R, exprimées en décibels ;
• l'unité de traitement 12 transmet alors à l'unité de contrôle 48 une nouvelle commande pour éteindre le synthétiseur de contrôle. L'opération de contrôle est ainsi achevée.

A control operation may consist in determining the losses of the coaxial cable 14. It then comprises, for example, the following steps:

• the processing unit 12 transmits to the control unit 48 of the reception unit 10 a command for switching off the set of mixer blocks MA to MD, for example by cutting off their power supply. The command is transmitted for example according to the protocol known under the brand DiSEq1. This is a data exchange protocol in only one direction, namely from the processing unit 12 to the reception unit 10. Its implementation is simpler than that of the protocol known under the brand DiSEq2 which is adapted to bidirectional data exchange between the processing unit 12 and the reception unit 10;
• one of the demodulation units DEMODA to DEMODD of the processing unit 12, or the single demodulation block, is controlled so as to extract from the signal received from the coaxial cable a signal at a determined fixed frequency, called the control frequency, for example 1700 MHz. We then check that the power of the signal received at the control frequency is very low;
• the processing unit 12 transmits to the control unit 48 a new command for the control synthesizer to provide the bandpass filter with a fixed frequency signal. The frequency of the signal received by the bandpass filter is slightly greater than the control frequency, for example 2 MHz to take account of a systematic frequency shift present at the demodulation block;
• the demodulation block of the processing unit 12 retrieves the signal again at the control frequency. The power of the signal received at the control frequency, or received power P _{R, is then determined} ;
• the attenuation of the cable is obtained by determining the difference between the power emitted at the output of the reception unit 10 (that is to say at the level of the connection between the reception unit 10 and the cable coaxial 14), called transmitted power P _T , and the received power P _R , expressed in decibels;
• the processing unit 12 then transmits to the control unit 48 a new command to turn off the control synthesizer. The control operation is thus completed.

• la valeur de la puissance transmise P_T correspond à une valeur prédéfinie fixée à l'avance. Bien que de conception particulièrement simple, la précision de l'atténuation ainsi déterminée est relativement faible ;
• plusieurs valeurs de la puissance transmise P_T à différentes fréquences sont stockées au niveau de l'unité de réception 10 et ces valeurs sont transmises par l'unité de réception à l'unité de traitement lors de l'opération de contrôle, par exemple en utilisant le protocole d'échange de données connu sous la marque DiSEqC 2 ;
• la valeur de la puissance transmise P_T est transmise par l'unité de réception 10 à l'unité de traitement 12 directement au moyen du synthétiseur de contrôle comme cela sera détaillé par la suite.

The transmitted power P _T can be determined in one of the following ways:

• the value of the transmitted power P _T corresponds to a predefined value fixed in advance. Although of particularly simple design, the accuracy of the attenuation thus determined is relatively low;
• several values of the transmitted power P _T at different frequencies are stored at the reception unit 10 and these values are transmitted by the reception unit to the processing unit during the control operation, for example by using the data exchange protocol known as DiSEqC 2;
• the value of the transmitted power P _T is transmitted by the reception unit 10 to the processing unit 12 directly by means of the control synthesizer as will be detailed hereinafter.

The present embodiment allows a simple way to determine the characteristics of the coaxial cable.

In addition, the attenuation control operation can be performed for several evenly distributed frequencies, for example with a pitch of 50 MHz. A processing is then performed on the received power values P _R to obtain a function representative of the received power P _R as a function of frequency. When the received power P _R is low for all the frequencies, this may correspond to a poor quality contact or to a malfunction of the reception unit. When the function representative of the received power P _R as a function of the frequency comprises ripples, this may correspond to poor impedance matching, to an incorrectly screwed connector, etc. When the received power P _R drops sharply as a function of frequency, this may correspond to a cable of poor quality. The processing unit may include an interface to indicate to a user the results of the control.

This embodiment also enables the receiving unit 10 to transmit data to the processing unit 12 even if it does not have a bidirectional data exchange protocol between the receiving unit and the unit. treatment, for example the protocol known as DiSEqC 2.

For example, the transmitted data may correspond to the average frequencies of the frequency subbands provided by the BPFA to BPFD bandpass filters. In this example, each frequency synthesizer of an MDA to MDD mixer block can provide a given frequency signal directly to the BPFA to BPFD bandpass filter associated with said mixer block. On receipt of an order transmitted by the processing, the control unit 58 controls the frequency synthesizers so that each frequency synthesizer provides the associated bandpass filter a signal whose frequency corresponds to the average frequency of the passband of the bandpass filter associated. The various fixed frequency signals are then added and the signal thus formed is transmitted on the coaxial cable. The values of the average frequencies are for example stored at the level of the control unit. The processing unit then scans the received signal over the entire transmission band to determine the average frequencies.

The transmitted data may also correspond to the transmitted power P _T. Only one control synthesizer is needed. Values of the transmitted power P _T by the reception unit 10 at different frequencies are in this case stored at the reception unit 10. The processing unit 12 transmits to the reception unit 10 a request which indicates a determined frequency for which the processing unit 12 wishes to know the transmitted power P _T by the reception unit 10. The control unit 48 then controls the control synthesizer so that it provides directly to the pass filter. associated band a first signal whose frequency, after division, is equal to the determined frequency. When the processing unit 12 has determined the frequency of the signal transmitted on the coaxial cable 14, it transmits to the reception unit 10 a continuation request. The control unit 48 then controls the control synthesizer so that it provides directly to the associated bandpass filter a second signal whose frequency, after division, is shifted with respect to the determined frequency. The offset between the determined frequency of the first signal and the frequency of the second signal is representative of the transmitted power P _T at the determined frequency.

Of course, the present invention is susceptible of various variations and modifications which will be apparent to those skilled in the art. In particular, the control unit 48 can be deleted, the control units 58 of the mixer blocks M, MA to MD being directly connected to the second control bus and directly receiving the signals transmitted by the processing unit 12.

Claims (10)

1. A receiver (10) that can receive several initial signals modulated in a same initial frequency band and/or distinct initial frequency bands and generate a signal modulated in a transmission band to be transmitted on a coaxial cable (14), characterized in that it comprises:

   focal points, associated with an antenna, each receive focal point being able to receive one of the initial modulated signal having a determined polarization;

   first mixers (35, 36, 37), each intermediary mixer (35, 36, 37) being capable of transforming the initial signal received by each receive focal point into an intermediary signal in an intermediary frequency band different from the transmission band;

   a selector (30) receiving the intermediary signals and capable of selecting several signals from among the received intermediary signals;

   for each selected signal:

   a second mixer (54) connected to a frequency synthesizer (57) capable of generating a determined mixing frequency and adapted to transforming the selected signal into a signal at least partly in the transmission band; and

   a bandpass filter (BPFA to BPFD) capable of extracting from the transformed signal a signal associated with a portion of the transmission band from among several at least partly distinct portions of the transmission band, the mixing frequency being a function of the portion of the transmission band and of the selected signal;

   means adapted to add the signals associated with the transmission band portions to form the signal modulated in the transmission band; and

   a control unit (48) capable of receiving control signals via the coaxial cable and driving the frequency synthesizers (57) according to the control signals for the generation of the corresponding mixing frequencies, and the selector (30) for the selection of the intermediary signals.
2. The receiver of claim 1, characterized in that the filters (BPFA to BPFD) are bandpass filters of distinct passbands (WA, WB), and wherein for a first filter, the passband of which is at frequencies greater than those of the passband of a second filter, the difference between the gain of the second filter and the gain of the first filter at the upper limiting frequency (f_ASUP) of the passband of the second filter is greater than 30 decibels and the difference between the gain of the first filter and the gain of the second filter at the lower limiting frequency (f_BINF) of the passband of the first filter is greater than 30 decibels.
3. The receiver of claim 1, characterized in that the frequency synthesizer (57) is adapted to provide a determined mixing frequency in a frequency band, the width of which being higher than the width of the initial frequency band or the sum of the widths of the distinct initial frequency bands.
4. The receiver of claim 1, characterized in that at least one frequency synthesizer (57) is adapted to transmit directly to the respective filter (BPFA to BPFD) a periodic signal at a predetermined frequency and power.
5. A method for transforming several modulated signals received in a same initial frequency band and/or distinct initial frequency bands into a signal modulated in a transmission band, characterized in that it comprises the steps of:

   receiving control signals via the coaxial cable;

   transforming each received modulated signal into an intermediary signal in an intermediary frequency band different from the transmission band;

   selecting several signals from among the intermediary signals as a function of control signals;

   for each selected signal, transforming the selected signal into a signal at least partly in the transmission band by mixing the selected signal with a mixing frequency, and extracting from the transformed signal by bandpass filtering a signal associated with a portion of the transmission band from among several portions of the transmission band, at least partly distinct the mixing frequency depending on the selected signal, on the portion of the transmission band and on control signal; and

   adding the signal associated with the transmissions and portions to form the modulated signal in the transmission band.
6. The method of claim 5, characterized in that each selected signal is amplified at a variable gain before being transformed and/or after having been transformed into a signal at least partly in the transmission band, the gain depending on the selected signal.
7. The method of claim 5 implemented by a receiver (10) according to claim 4, linked, by means of the coaxial cable (14), to a processing unit (12) adapted to process the signal modulated in the transmission band provided by the receiver in normal operation, further comprising:

   the transmission from the processing unit to the receiver of a request related to a determined frequency;

   the transmission from the receiver of a periodic signal corresponding to the receipt by the processing unit if a periodic signal at the determined frequency;

   the determination by the processing unit of the power of the received periodic signal at the determined frequency; and

   the determination by the processing unit of the power attenuation of the coaxial cable from the power of the received periodic signal at the determined frequency and the power of the periodic signal transmitted by the receiver.
8. The method according to claim 7, characterized in that the receiver (10) transmits successively through the coaxial cable (14), upon receipt of requests from the processing unit (12), periodic signals at different fixed frequencies.
9. The method according to claim 7, wherein the receiver (10) provides through the coaxial cable (14) a periodic signal at a first frequency corresponding to the receipt by the processing unit (12) of a periodic signal at the determined frequency, and a periodic signal at a second frequency different from the first frequency, the difference between the first and the second frequencies being representative of the power of the periodic signal at the first frequency transmitted by the receiver.
10. The method according to claim 7, characterized in that each frequency synthesizer (57) of the receiver (10) is adapted to transmit directly to the respective filter (BPFA to BPFD) a periodic signal, and wherein the receiver transmits to the processing unit (12), through the coaxial cable (14), a signal corresponding to the sum of periodic signals provided by the frequency synthesizers, each periodic signal being at frequency equal to the average frequency of one of the portions of the transmission band.

Images